In OSPF, routers exchange link-state information in different stages to establish full adjacency. The MTU size is checked during the Exchange state.
Step-by-Step Breakdown:
1. OSPF Adjacency Process:
o OSPF routers go through multiple stages when forming an adjacency: Down, Init, 2-Way, ExStart, Exchange, Loading, and Full.
2. Exchange State:
o During the Exchange state, OSPF routers exchange Database Description (DBD) packets to describe their link-state databases. The MTU size is checked at this stage to ensure both routers can successfully exchange these packets without fragmentation.
o If there is an MTU mismatch, the routers may fail to proceed past the Exchange state.
Juniper Reference:
· MTU Checking in OSPF: Junos uses the Exchange state to check for MTU mismatches, ensuring that routers can properly exchange database information without packet fragmentation issues.
